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Sludge Deserves a Closer Look

Each year in the United States alone, several million tons of treated sewage are added as fertilizer to farm fields, parks, golf courses, and other land. That has raised a ruckus with neighbors who object to the stink and say they fear for their health. Almost a decade ago, the Environmental Protection Agency (EPA) set standards for chemical and bacterial content in the treated sewage. Now, the National Research Council (NRC) says the agency needs to learn more about the health risks of the sludge and update its standards.

Sludge comes from sewage that has been treated in wastewater plants. Once processed further, it earns the dubiously more pleasant label "biosolids" and can be sold for fertilizer. The additional processing was first required in 1993, when EPA set limits on nine inorganic chemicals and specified how to reduce bacteria. As mandated by the Clean Water Act, the agency in 2000 asked the NRC to review its standards and how well they protect public health.

The committee found no evidence that biosolids are a threat, but it noted that there's been scant research on health effects. "We really had an information void," says committee chair Thomas Burke, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore. To fill those gaps, the committee recommends that EPA begin a range of research from studying workers who apply biosolids to undertaking a new national survey of sewage sludge that would identify more chemicals and use higher tech methods for identifying pathogens than did the most recent survey in 1988. Additionally, EPA should also use more modern risk-assessment methods to set its standards.

In a statement, EPA defended its biosolid standards: "The agency believes existing standards adequately protect public health but also shares the academy's view that additional scientific research and data gathering would be helpful."